1. Field of the Invention
The field of the invention relates to plethysmograph systems, and seals for providing an air-tight closure between the cover and lid of a plethysmograph and for sealing off tubes and/or cables extending into the air-tight chamber of such an apparatus.
2. Brief Description of the Prior Art
Plethysmograph systems have been developed for monitoring the pulmonary functions of both infants and adults. A pair of such systems are described in U.S. Pat. Nos. 4,671,297 and 4,972,842, the latter of which is incorporated by reference herein.
The flow through a plethysmograph is used for monitoring patient ventilation, usually in ICU (intensive care unit) settings. The plethysmograph includes a sealed chamber in which a patient is placed. The tidal volume of air inspired and expired through the ventilator tubing causes volume displacements from the plethysmograph to the atmosphere through a flow resistive leak. The rise and fall of pressure within the plethysmograph can then be related to the amount of air displaced with each breath, allowing the measurement of tidal volumes.
A plethysmograph is usually configured as a box that has a hinged wall or lid with a rubber gasket or seal around the perimeter thereof. The preferred arrangement in patient settings is for the plethysmograph to be constructed in a "clamshell" configuration where the top and the bottom of the box are not of equal depth. This way, when the plethysmograph is opened, the patient is not recessed or difficult to access but is right at the surface of the opening.
As described in U.S. Pat. No. 4,972,842, the flow through a plethysmograph system for monitoring neonates in the intensive care setting requires an airtight seal. Typically, the patient is subject to supportive therapies that include intravenous administration of drugs, plasma or various electrolytes. While it is possible to disconnect IV tubes and reconnect them across bulkhead fittings that feed through an airtight seal, this approach is flawed for many reasons. Firstly, the possibility of introducing air bubbles, violating sterility or clotting blood are reasons not to break and reconnect an IV tube. Furthermore, to require this type of connection every time the patient is introduced to or removed from the plethysmograph would be a strong disincentive to the use of the flow through plethysmograph in an ICU setting.